Carefully slice the cucumber and enough onion to make a quarter cup on the thinnest setting of a mandoline. Or slice paper thin with a knife.

Place in a bowl and toss with a squeeze of lemon juice.

Whisk together remaining ingredients. Pour over cucumbers and onions.

Toss together, separating cucumbers as much as you can.

Allow to chill in the fridge for 2-3 hours before serving.